Balanced detectors



July 19, 1955 F. A. JENKS El AL BALANCED DETECTORS 2 Sheets-Sheet 1 Filed Feb. 27, 1951 IND/O4TO/2 AMPL/F/E/Z Y 5 mm m w fi WAR A KN W W ms mN IND/CATO]? FIG. 5

July 19, 1955 F. A. JENKS ET AL I 2,713,636

' BALANCED DETECTORS Filed Feb. 27, 1951 2 Sheets-Sheet 2 will,

United States Patent 2,713,636 BALANCED DETECTORS Application February 27, 1951, Serial No. 212,932 6 Claims. (Cl. 250-=-31) This invention relates to balanced detectors for detecting microwave energy in wave guides.

Heretofore it has been customary to make a wave guide-coaxial transition unit and then locate the detectors in the coaxial arms in order to obtain a good match. Usually a magic tee configuration is used to get push-pull injection of the signal and parallel injection of the local oscillator output. This technique, however, is space consuming and, therefore, not suitable for compact equipment design.

Such a compact design could be achieved by locating the detectors on or in the wave guide. In order to obtain a balanced output from the detectors they are introduced in the same plane transverse to the wave guide. The introduction of the detectors modifies the impedance of the Wave guide. This impedance must be balanced by one of equal amount and opposite sign. a balancing impedance is created by inserting a screw in the wave guide in the same plane as the detector and from the opposite wall. This screw serves another purpose. The protruding detector tends to set up a resonant path for the microwave energy within the wave guide. The screw breaks this path up and broadens the frequency response curve of the device.

A cross bar of conductive material is mounted across the Wave guide in the same plane as the detectors and the detectors connected to this cross bar. For parallel-connected D. C. output this cross bar is solid. For seriesconnected D. C. output a more complicated structure is used for the cross bar. The last-mentioned cross bar is formed of a rod and two concentric tubes supported on the rod but insulated from it by suitable insulating material. Thus the parts are insulated from each other at D. C. and connected at radio frequencies. Small R. F. by-pass capacitances are built into the D. C. series cross bar to keep the microwave energy and the D. C. current along the respective proper paths.

The result is a broad band match with a voltage standing wave ratio under two to one over such a range of frequencies as 4200 to 4400 megacycles. This is accomplished with a small compact device not requiring carefully selected crystals but permitting the signal to be ap-- plied push-pull and the oscillator energy in parallel to the detectors.

Other and further advantages of this invention will be apparent as the description thereof progresses, reference being had to the accompanying drawings, wherein:

Fig. l is an isometric view of one embodiment of the invention;

Fig. 2 is an isometric view of another embodiment of the invention as modified for the D. C. series connection of the crystals;

Fig. 3 is a section taken along the line 33 of Fig. 2;

Fig. 4 is a schematic diagram of the D. C. equivalent circuit of the parallel-connected embodiment; and

Fig. 5 is a schematic diagram of the D. C. equivalent circuit of the series-connected embodiment.

In Fig. 1 a wave guide is represented generally by the 72 of insulating material.

reference number 10. A crystal detector 11 is inserted into the top surface 12 of the wave guide 10 by means of a crystal holder 14. A second crystal detector 15 is inserted into the bottom surface 16 of the wave guide 10 by means of a second crystal holder 17. These crystals are positioned in a common transverse plane and displaced from the vertical center line 18 of the plane by an equal amount. The detector units are described herein as crystals but they could also be electrical discharge devices and bolometers with suitable modifications.

The tip 20 of each crystal i1 and 15 is set in cylindrical contactors 2i and 22, respectively, which are electrically and mechanically connected to a cross bar 23 of conductive material. This cross bar is fixed in the walls 24 and 25 of the wave guide along the middle of the above-mentioned transverse plane. The center conof cross bar 23. This coaxial line serves to introduce energy from the local oscillator for mixing purposes.

in order to counteract the resonant effects of each crystal El and 15, as explained above, anti-resonant posts 28 and 30 are placed in the wave guide walls 16 and 12, respectively, opposite each crystal 11 and 15.

The distinction between the series and parallel arrangements will be best understood with reference to the schematic diagrams of Figs. 4 and 5. Fig. 4 shows the parallel arrangement with crystals 11 and 15. It will be seen that the crystals are connected back-to-back with the common point 33 connected to ground. The other ends of the crystals are connected through coaxial cables 34 and 35, respectively, to the primaries 36 and 37 of transformers 38 and 39, respectively. The other terminals 46 and 41 of the primaries are connected in series through a potentiometer with a movable contact 43 connected to ground. The purpose of this potentiometer 42 is to assure that the currents through the two pri maries 36 and 3-7 are equal. The secondaries 4d and 45 have terminals 46 and 47 connected together and to a reference potential. The other terminals 48 and :9 are connected, respectively, to the inputs 50 and 51 of the amplifier 52 associated with the detector circuit 53.

In the series arrangement the crystals 61 and 62 are connected in series with a point 54 between them connected to ground. The primaries 55 and 56 of the trans formers 57 and 58 are connected in series with each other and the crystals 61 and 62. The secondaries 59 and 66 are connected in series and to the input of the amplifier of the detector circuit 53.

It will be seen from Fig. 1 that one terminal 2% of each crystal l1 and 15 is connected to the cross bar 23, corre sponding to the common point 33 of Fig. 4. The other ends of the crystals 11 and 15 are brought out separately to the center conductors of coaxial lines 3:5 and respectively, through connectors 14 and 17. The details of a suitable connector for this purpose are shown in Fig. 3 and will be described later.

The physical arrangement of the D. C. series modiii cation is shown in Figs. 2 and 3. in this modification the crystals 61 and 62 are inserted into receptacles 63 and 64, respectively, on the special cross piece 65 mounted in the walls 66a and 66b of the wave guide 66. This cross piece 65 is formed of two pieces of tubing 67 and 63 held together by a double-ended screw 79. Each threaded end in a tapped hole 71 in a plug The threaded ends of screw '70 are each one-quarter wave length long and form an open transmission line with their respective tubes 67 and 68. Each of these plugs 72 fits inside its respective tube 67 or 68, and rests against a ridge 73 extending radially inward from the inside surface of the tubes 67 and 63. As the plugs 72 are pulled together by action of the screw 70, they carry with them the tubes 67 and 68 because of the-ridges 73. The outer end 74 is threaded to receive a spreading plug 75 of conductive material. The tube ends are also split by saw cuts 76 to permit a spring contact to be made with a plug 77 of conductive material. These plugs 77 are adapted to receive the center conductor 7e of a coaxial cable central head 31 of the screw 7-3 is insulated from the tub-cs 67 and by ashers of insulating material to form a capacitive path for the microwave energy between the central head tilt and the tubes 67 and 6% while preventing the flow of direct current between these parts. This or pacitive path is reenforced by a low impedance from the quarter wave open-circuited transmission line formed by the tubes 67 and 63 and the screw 7il. The center condoctor 83 of a coaxial cable is electrically connected to the head 35. of the screw 7%. The end of the t be 67 received in a hole 34 in a bushing 85 of com. ive mate rial inserted into the wave guide wall 66:1. T hole 54 is lined with an insulating material 43a, such as polystyrene tape. expansion plug 75, as it scrr down into the tube 67, expands the tube to form .gh mechanical contact with the bushing while insulated from it by the insulation Sen. This forms capacitive path for microwave energy while isolating the direct current. The plug 77 is set in a cap 86 of insulating material which is itself set in a cap 3'7 of conductive material that receives the coaxial cable ill) and is a tached to the bushthrough the threaded connector 8%) by threads 99. The other end of the cross bar 65 is connected to a coaxial cable Si by similar means.

Radio l requency energy is prevented from propagating out along cables 30 and 89 by the quarter wave open transmission line formed by the screw 70 and the tubes 67 and 63.

This connector cap construction, together with the special construction oi the cross bars 67 and till, prevents any leakage of microwave energy down the cable lit). The tight mechanical connections of the screw 7t? with the sleeves 6'7 and 68 and of the sleeves 6'7 and 68 to the bushing 85, while at the same time providing a capacitive path through insulated washers 82 and 84:1, prevent microphonics in the circuit as would be caused by looser mechanical connections when the equipment was used in the presence of considerable vibration as in mobile equipment.

The crystal 6i is inserted through the wave guide wall 666 by means of a bushing 91 of conductive material adapted to receive an insert member 92 separated from the bushing by a layer 93 of insulating material, such as polystyrene tape. When the crystal 61 is inserted in the bushing 51, it is electrically connected to the central conductor 94 of the coaxial cable 95 through a cap 96 of conductive material adapted to receive the central conductor M and a spring 97 of conductive material fitted into a recess 98 in the cap 96. The cap 6 and spring 97 are pressed down on the crystal 61 by a cap 160 that is fastened to the bushing 91 by a threaded sleeve member 101 and insulated from the cap 96 by an annular ring 1% and a disk lilfi, both made of insulating material. The second crystal 62 is similarly mounted in the wave guide and connected between tube 63 and the coaxial cable 89. This construction provides a rigid microphonic free mounting for the detector element while providing a short-- ing path through insulation 93 for any microwave energy that might otherwise leak out along cable 95.

In addition to the cross bar 65 and the crystals 61 and 2, a matching post 104 for matching the impedance of the crystals and cross bar is introduced into the field. This matching post, preferably a metallic plug, is inserted into wall 66d of the wave guide 66 along the center line of the wide dimension and at a quarter wave length in front of the crystals 61 and 62. In addition, anti-resonant posts 185 and 106 are mounted one on each wall 66c and 66a in the same plane with the crystals 61 and 62 and displaced from the center by approximately equal amounts of each tube 67 or 68 The but in the opposite direction in order to balance out the reactance added by the insertion of the crystals and to broaden the band width over which the equipment may he used effectively, as explained above.

in the series resonant structure shown in Figs. 2 and 3, there are two D. C. paths. One runs from the coaxial cable it through plug 77, tube 67, connector 63, crystal 6i, spring 97 and coaxial cable 95. The other D. C. path runs from coaxial cable it) through the connector 107, tube 68. crystal connector 64, crystal 6?. and its associated co; .1 cable. These two paths may be connected in series, if desired, or used separately. The series connection of the crystals 61 and 62 shown in Fig. 5 is represented in Figs. 2 and 3 by the coaxial cable the cow nector plug '77, tube 67, connector 63. crystal (:1. connector structure 96., 97 and coaxial cable which may be connected to coaxial cable as of Fig. 2, and through connector assembly 1.67 to tube 68 through connector 64 to crystal 62;. The output of these two crystals in series may connected to the input of an indicator device 53 directly as shown in Fig. 5 or through an amplifier 52 as shown in Fig. 4.

The series structure shown in Figs. 2 and 3 can also be connected for parallel operation of the crystals by connecting both lines Sil and 39 together and to ground and the rectifiers 61 and 62 to an external circuit. The connections could also be reversed. The rectifiers 61 and 62 could be connected together and to ground with the lines 8 and 8t connected to the external circuit.

The coaxial center conductor 83 is fed from a local oscillator, and at a particular instant produces voltage vectors in the directions indicated by arrows 108 and lit The energy in the wave guide could be energy picked up by a receiving antenna, such as a horn (not shown), and led into the wave guide 66, to produce an electrical vector at that instant in the direction indicated by arrows ill in Figs. 1 and 2, which is in phase with the vector 1111' of local oscillator energy in the upper portion of the guide, but 180 degrees out of phase with the local oscillator energy vector indicated by the arrows 108 in the lower portion of the wave guide. The result would be that the vector ditlerence in energy is transmitted through the lower crystal l5, and the vector sum of the energies through the upper crystal 11 in the D. C. parallel version of Fig. l. When the directions of the vectors reverse on the next alternation. the lower crystal 15 would conduct the vector sum of the energies and the upper crystal 11, the vector difference of the energies. In the series case illustrated in Figs. 2, 3 and 5, local oscillator energy produces vectors in the direction of arrows 108 and 110 to set up currents through the crystals 61 and 62 outward from the central nut 81. When the vectors reverse on the next alternation, the polarities are wrong for conduction through the crystals and little or no current flows.

Obviously, the present invention could be applied wherever it is required to extract and rectify energy from a wave guide over a wide band of frequencies and with a maximum of efficiency for a minimum of bulk and weight of equipment.

This invention is not limited to the particular details of construction, materials and processes described, as many equivalents will suggest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

l. A balanced detector of electromagnetic energy comprising a section of waveguide, a conductive rod mounted between and electrically contacting the conductive walls of the waveguide, a pair of detector elements mounted on but insulated from the waveguide with one end of each in electrical contact with said rod inside said waveguide and their axes of conduction in the same transverse plane as the rod and perpendicular to it, and means to apply high frequency energy to the center of the rod.

2. A balanced detector of electromagnetic energy comprising a section of waveguide, a conductive rod mounted between and electrically contacting the conductive walls of the waveguide, a pair of detector elements mounted on but insulated from the waveguide with one end of each in electrical contact with said rod inside said wave guide at points displaced equally from the center of said rod and their axes of conduction in the same transverse plane as the rod and perpendicular to it, and means to apply high frequency energy to the center of the rod.

3. A balanced detector of electromagnetic energy comprising a section of waveguide, a conductive rod mounted oetween but insulated from the side walls of the waveguide, a pair of conductive tubes mounted concentrically on but insulated from said conductive rod, a pair of detector elements mounted with one end of each in electrical contact with an associated one of the tubes and their axes of conduction in the same transverse plane as the rod and perpendicular to it, and means to apply highfrequency energy to the center of the rod.

4. A balanced detector of electromagnetic energy comprising a section of waveguide, a conductive rod mounted between but insulated from the side walls of, the waveguide, a pair of conductive tubes mounted concentrically on but insulated from said conductive rod, a pair of detector elements mounted with one end of each in electrical contact with an associated one of the tubes appoints displaced equally from the center of said rod and their axes of conduction in the same transverse plane as the rod and perpendicular to it, and means to apply high frequency energy to the center of the rod.

5. A balanced detector of electromagnetic energy comprising a section of waveguide, a conductive rod mounted til between and electrically contacting the conductive walls of the waveguide, a pair of detector elements mounted with one end of each in electrical contact with said rod inside said waveguide at points displaced equally from the center of said rod and their axes of conduction in the same transverse plane as the rod and perpendicular to it, means to counteract the unbalance introduced into the electromagnetic field by the detecting elements, and means to apply high frequency energy to the center of the rod.

6. A balanced detector of electromagnetic energy comprising a section of waveguide, a conductive rod mounted between but insulated from the side walls of the waveguide, a pair of conductive tubes mounted concentrically on but insulated from said conductive rod, a pair of detector elements mounted with one end of each in electrical contact with an associated one of the tubes at points displaced equally from the center of said rod and their axes of conduction in the same transverse plane as the rod and perpendicular to it, means to counteract the unbalance introduced into the electromagnetic field by the detecting elements, and means to apply high frequency energy to the center of the rod.

References Cited in the file of this patent UNITED STATES PATENTS 2,413,939 Benware Jan. 7, 1947 2,420,892 McClellan May 20, 1947 2,469,222 Atwood May 3, 1949 2,527,910 Braden Oct. 31, 1950 2,550,524 Braden Apr. 24, 1951 2,552,052 Matare May 8, 1951 2,576,481 Rodwin Nov. 27, 1951 

